1. Field of the Invention
The present invention relates to micromechanically produced valves and especially to piezoelectrically operated micro-valves.
2. Description of Prior Art
Microvalves can generally be used in the fields of pneumatics and fluidics for controlling the flow of gases and liquids, i.e. fluid flows. Such a valve can either have the function of a pilot valve or it can directly be used for controlling a volume flow or a pressure in a working piston or the like.
Piezoelectrically operated microvalves which are known at present and which are based on the inverse piezoelectric effect comprise a large piezoelectric ceramic which is fixed at one end in most cases and by means of which the fluid flow is controlled directly. Such a piezoelectrically operated silicon microvalve is described in R. Rossberg, B. Schmidt, S. Buttgenbach: "Micro Liquid Dosing System", Microsystem Technologies 2 (1995), pages 11 to 16, Springer-Verlag 1995. In such microvalves, either the piezoelectric ceramic itself can serve as a valve tappet or the valve tappet used is a tappet which is directly guided by the piezoelectric ceramic.
The microvalves described in the above publication are disadvantageous insofar as, for obtaining the deflection of the valve tappet over the valve seat which is necessary for a high flow rate, a very long piezoelectric ceramic is required, said valve tappet being also referred to as valve flap. For accommodating such a piezoelectric ceramic, it is, of course, also necessary to use a correspondingly large casing. It follows that the known piezo-operated microvalves, which are described e.g. in the above-mentioned publication, have, in comparison with their construction size, a comparatively small valve opening, i.e. nominal width.
From A. Dogan, J. F. Fernandez, J. F. Tressler, K. Uchino, R. E. Newnham: "Properties of piezoelectric actuators"; Proceedings 5th International Conference on New Actuators 1996; Bremen Jun. 26th to 28th 1996, and J. F. Fernandez, A. Dogan, J. F. Tressler, K. Uchino, R. E. Newnham: "Tailoring performance of cymbal actuators", Proceedings 5th International Conference on New Actuators, Bremen Jun. 26th to 28th 1996, piezoelectric actuators are known, which consist of a piezoelectric ceramic material as a drive element which is arranged between two end covers having their edges connected to the ceramic material. By means of this arrangement, a lateral movement of the piezoelectric ceramic is converted into a large axial displacement at right angles to said end covers and amplified. As has been described in the publication "Tailoring performance of cymbal actuators", metals or metal alloys, e.g. zirconium, brass, low-carbon steel, molybdenum or tungsten, are used as end covers.
The Abstract of JP-A-07158757 discloses a microvalve comprising a base element provided with a passage opening which is adapted to be closed by means of a portion of increased thickness of a silicon diaphragm. The silicon diaphragm has attached thereto a piezoelectric actuator by means of which said silicon diaphragm can be displaced for opening and closing the passage opening. FR-A-2642812 describes a microvalve in which a tappet member is supported by means of piezoelectric diaphragmlike components, which are provided with planar electrodes, in such a way that a passage opening can be opened and closed by means of the tappet member.